HOW TO ADD AN EXISTING PRIVATE SSH KEY TO USERS ON LINUX
When trying to use a private key as a new user, you must first create a .ssh directory for that new user, followed by creating an authorized_keys file inside of that .ssh directory for the user. Then, copy the key stored inside the authorized_keys file inside the .ssh directory under the /root directory.
Inside of the new user’s /home directory, create a directory called ‘.ssh’ by typing:
(The .ssh folder will be a hidden folder, and can only be seen by running ‘ls -a’)
Inside the .ssh directory run by typing:
From your /root directory, run the following command:
cat /.ssh/authorized_keys >> /home/username/.ssh/authorized_keys
This will append what you have in /root’s authorized_keys file to the specified user’s authorized_keys file, allowing your new user access via private SSH.